• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.264.1-264.1
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• 2013

Graphene is a two-dimensional carbon material whose structure is one-atom-thick planar sheet of sp2-bonded carbon atoms densely packed in a honeycomb crystal lattice. It has drawn significant attention with its distinguished structural and electrical properties. Extremely high mobility and a tunable band gap make graphene potentially useful for innovative approaches to electronics. Although mechanical exfoliation of graphite and decomposition of SiC surfaces upon thermal treatment have been the main method for graphene, they have some limitations in quality and scalability of as-produced graphene films. Solutionphase and solvothermal syntheses of graphene achieved a major improvement for processing, however for device fabrication, a reproducible method such as chemical vapor deposition (CVD) growth yielding high quality films of controlled thickness is required. In this research, we synthesized hexagonal graphene flakes on Cu foils by CVD method and controlled its coverage, density and the size of graphene domains by changing reaction parameters. It is important to control these parameters of graphene growth during synthesis in order to achieve tunable properties and optimized device performance.

• Journal of the Korean Ceramic Society
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• v.45 no.5
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• pp.280-284
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• 2008

In order to investigate residence time effect on the growth of ZrC film, the ZrC films grew with various system total pressure (P) and total flow rate (Q) by low pressure chemical vapor deposition because residence time is function of system total pressure and total flow rate. Thermodynamic calculations predict that the decomposition of source gases ($ZrCl_4$ and $CH_4$) would be low as increasing the residence time. Thermodynamic calculations results were proved by investigating deposition rate with various residence time. Deposition rate decreased with residence time of source gas increased. Besides, depletion effect accelerated diminution of deposition rate at high residence time. On the other hands, the deposition rated was increased as decreasing the residence time because fast moving of intermediate gas species decrease the depletion effect. The crystal structure was not changed with residence time. However, the largest size of faceted grain showed up to specific residence time and the size of grain was decreased whether residence time increase or not.

• Korean Journal of Materials Research
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• v.28 no.5
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• pp.279-285
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• 2018

Graphene is an interesting material because it has remarkable properties, such as high intrinsic carrier mobility, good thermal conductivity, large specific surface area, high transparency, and high Young's modulus values. It is produced by mechanical and chemical exfoliation, chemical vapor deposition (CVD), and epitaxial growth. In particular, large-area and uniform single- and few-layer growth of graphene is possible using transition metals via a thermal CVD process. In this study, we utilize polystyrene and boron oxide, which are a carbon precursor and a doping source, respectively, for synthesis of pristine graphene and boron doped graphene. We confirm the graphene grown by the polystyrene and the boron oxide by the optical microscope and the Raman spectra. Raman spectra of boron doped graphene is shifted to the right compared with pristine graphene and the crystal quality of boron doped graphene is recovered when the synthesis time is 15 min. Sheet resistance decreases from approximately $2000{\Omega}/sq$ to $300{\Omega}/sq$ with an increasing synthesis time for the boron doped graphene.

• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.122-122
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• 2000

Magnesium oxide is thermodynamically very stable, has a low dielectric constant and a low refractive index, and has been widely used as substrate for growing various thin film materials, particulary oxides of the perovskite structure. There has been a considerable interest in integrating the physical properties of these oxides with semiconductor materials such as GaAs and Si. In this regard, it is considered very important to be able to grow MgO buffer layers epitaxially on the semiconductors. Various oxide films can then be grown on such buffer layers eliminating the need for using MgO single crystal substrates. Vapor phase epitaxy of magnesium oxide has been accomplished on Si(001) substrates in a high vacuum chamber using the single precursor methylmagnesium tert-butoxide in the temperature range 750-80$0^{\circ}C$. For the epitaxy of the MgO films, SiC buffer layers had to be grown on Si(001). The films were characterized by reflection high energy electron diffraction (RHEED) in situ in the growth chamber, and x-ray diffraction (XRD), x-ray pole figure analysis, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS) after the growth.

• Korean Journal of Materials Research
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• v.10 no.3
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• pp.241-245
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• 2000

Thick GaN films were grown on (0001) sapphire substrates using the direct reaction gallium and ammonia. The GaN films grew dominantly along [0002] direction, but included the growth of GaN(1010) planeq with V-shaped facetted surfaces at low temperature. With increasing growth temperature, however, the growth of GaN (1010) and (1011) planes was appeared from the films, which gives rise to the growth of hexagonal crystal with pyramid-shaped surface. The growth rate of GaN films increased with increasing growth temperature, but decreased at $1270^{\circ}C$ because the GaN films began to decompose into Ga and N at the temperature. It seemed that the crystal and optical qualities of the GaN films improve with increasing $NH_3$ flow rate. From X-ray diffraction (XRD) and photoluminescence (PL) measurements, it was observed that the yellow luminescence (YL) appeared to be significant as the peak intensity of (1010) plane of XRD spectra increased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.26 no.12
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• pp.863-866
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• 2013

SiC crystal ingots were grown on 6H-SiC dual-seed crystals with different surface roughness and different seed orientation by a PVT (Physical Vapor Transport) method. 4H and 15R-SiC were grown on seed crystal with high root-mean-square (rms) value. The polytype of grown crystal on the seed crystal with lower rms value was confirmed to be 6H-SiC. On the other hand, all SiC crystals grown on seed crystals with different seed orientation were proven to be 6H-SiC. The surface roughness of seed crystals had no effect on the crystal structure of the grown crystals. However, the crystal quality of 6H-SiC single crystals grown on the on-axis seed were revealed to be slightly better than that of 6H-SiC crystal grown on the off-axis seed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.2
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• pp.85-92
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• 2010

$SF_6$ gas has been widely used in many industrial fields as insulating, cleaning and covering gases due to its outstanding arc-extinguishing and insulating properties. However, global warming potential of $SF_6$ gas is 23,900 times more than that of $CO_2$ and it remains in the air during 3,200 years. For these reason, technological and economical effects could be expected for the separation of $SF_6$ from gas mixtures by hydrate forming process. In this study, we carried out morphological studies for the $SF_6$ hydrate crystal to understand its formation and growth mechanisms. $SF_6$ hydrate film was initially formed at the interfacial boundary between gas and liquid regions, and then subsequent dendrite crystals growth was observed. The dendrite crystals grew to the direction of gas region probably due to the guest gas concentration gradient. The detailed growth characteristics of $SF_6$ hydrate crystals such as nucleation, migration, growth and interference were discussed in this study.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1999.06a
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• pp.285-303
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• 1999

Thin films of hydrogenated amorphous silicon carbide compounds (a-SixC1x:H) of different compositions were deposited on Si substrate by RF plasma-enhanced chemical vapor deposition (PECVD). Experiments were carried out using silane(SiH4) and methane(CH4) as the gas precursors at 1 Torr and at low substrate temperature (25$0^{\circ}C$). The gas flow rate was changed with every other parameters (pressure, temperature, RF power) fixed. The substrate was Si(100) wafer and all of the films obtained were amorphous. The bonding structure of a-SixC1x:H films deposited was investigated by X-ray photoelectron spectroscopy (XPS) for the film compositions. In addition, the surface morphology of films was investigated by atomic force microscopy (AFM).

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.39-42
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• 1999

Nitrogen-doped SiC(3C) (N-SiC(3C)) epliayers were grown on Si(111) substrate at $1250^{\circ}C$ using chemical vapor deposition (CVD) technique by pyrolyzing tetramethylsilane(TMS) in $H_{2}$ carrier gas. SiC(3C) layer was doped using $NH_{3}$ during the CVD growth to be n-type conduction. Physical properties of N-SiC(3C) were investigated by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) patterns, Raman spectroscopy, cross-sectional transmission electron microscopy (XTEM), Hall measurement, and current-voltage(I-V) characteristcs of the N-SiC(3C)/Si(p) diode. N-SiC(3C) layers exhibited n-type conductivity. The n-type doping of SiC(3C) could be controlled by nitrogen dopant using $NH_{3}$ at low temperature.

• Journal of the Korean Vacuum Society
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• v.1 no.1
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• pp.126-133
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• 1992

This study deals with the crystal growth and the optical characteristics of CdS thin films activatedby silver. CdS:Ag thin films were deposited by using an electron beam evaporation(EBE) technique in vacuumof 1.5X 10-'torr, voltage of 4 kV, current of 2.5 mA and substrate temperature of 250$^{\circ}$C CdS:Ag photoconductivefilms prepared by EBE method show high photoconductivity after annealing at about 550"c for 0.5 h in air andAr gas.The grain size of CdS:Ag thin films annealed in Ar atmosphere (1 atm) was grown over 1 ym and the thicknessof the films is 4-5 pm. The analysis of X-ray diffraction patterns shows that the crystal structures are hexagonal.The diffraction line by (00.2) plane can only be observed, indicating that c-axis of hexagonal grows preferentiallyperpendicular to the substrate. The profiles of photoluminescence spectra of CdS:Ag films show Gaussian typecurves at room temperature, the maximum peak spectral sensitivity of CdS:Ag is located at the wavelength of520 nm.We annealed CdS:Ag thin films in air and Ar vapor in order to make the CdS photoconductors having theintensive photocurrent, the broad distribution of the photocurrent spectrum and the large value of the ratioof the photocurrent (pc) to the dark current(dc). We found that CdS:Ag thin films annealed in air atmospherewas the best one.air atmosphere was the best one.